Synchrotron-based VUV excitation-induced ultrahigh quality cool white light luminescence from Sm-doped ZnO

We report that the rare-earth (RE) ion, Sm-doped ZnO, acts as white light emitting vacuum ultraviolet (VUV) phosphors and possesses an ultrahigh color rendering index (CRI) and color quality scale (CQS). The VUV-excited emission spectra measured from the synchrotron source reveal the emergence of multi-color emission bands in the visible-IR region and substantially depend on the concentration of Sm³⁺ ions. A mechanism is proposed to elucidate the origin behind the high-energy bandgap excitation of the host charge carrier and subsequent energy transfer to the Sm³⁺ states leading to additional green-yellow-orange emission bands of Sm³⁺(⁴G_5/2→⁶H(J=5/2,7/2,and9/2)). High-quality cool white light (correlated color temperature 5600 K) having CIE coordinates (0.33, 0.35) with a CRI as high as 95.89 and a CQS value of 94.49 is achieved for Zn_0.985Sm_0.015O under synchrotron VUV radiations. This Letter demonstrates that RE activated ZnO-based phosphors are expected to be a promising candidate in solid state lighting, as well as plasma display devices.